The present invention relates to a radial support for a cryostat containing a superconducting magnetic resonance imaging magnet.
A cryostat is a containment vessel designed to thermally isolate its interior from exterior ambient temperature conditions. To achieve the desired degree of thermal isolation, multiple nested vessels may be employed with each vessel functioning as one of a sequence of temperatures, with the interior temperature of the innermost vessel being the coldest. The inner vessels need to be supported and spaced apart from one another with sufficient rigidity to withstand shipping loads yet have few physical connections between the interior vessels and the external vessels.
In an embodiment of the present invention, the radial suspension is used with a self shielded superconducting magnet. The superconducting magnet is located in the innermost vessel and is a key component in magnetic resonance imaging and spectroscopy. The superconducting magnet produces a uniform magnetic field in the bore of the magnet to align the nuclei of the subject being evaluated. In a self shielded magnet it is important from the standpoint of magnet field homogeneity that the magnet remain stationary with respect to the outer vacuum vessel which in the self shielded magnet also serves as the shield. Previous suspension systems, such as the one described in U.S. Pat. No. 4,516,405 assigned to the same assignee as the present invention are not symmetric with respect to the outer vacuum vessel vertical and horizontal centerlines. This lack of symmetry could result in a significant amount of movement of the axial centerline of the vessel containing the superconducting magnet relative to the outer vacuum vessel axial centerline as a result of thermal expansion induced in the outer vacuum vessel by as small a temperature change as five degrees Fahrenheit.
It is an object of the present invention to provide a radial suspension system which is sufficiently strong to withstand shipping loads yet have as few physical connections to the cryostat as possible to reduce thermal conduction and radiation heat leaks.
It is a further object of the present invention to provide a suspension system for use with a self shielded magnet which minimizes movement of the magnet relative to the shield due to temperature changes.